Telecommunications carriers (e.g., long distance providers) continually strive to increase the reliability of their communications networks. They do this, in part, by increasing the speed by which they can restore network operation following failure in one or more components of the network. A communications network consists of a collection of transmission links, also known as segments, that are interconnected at network nodes. The segments include transmission lines, fiber optic cables, microwave links, and other such transmission medium. Traffic is transmitted on the network from one endpoint to another endpoint through a current route or "trunk," which is a network path of segments that interconnect the endpoints. The network nodes may serve a variety of functions such as amplifying the network traffic for transmission down the next segment in the route or establishing an interconnection between two segments connected to the node (i.e., a switch). The restoration nodes can be controlled locally or from a remote computer system to connect or to disconnect segments that are connected to the node.
Unfortunately, the components (e.g., nodes and segments) of the communications network may occasionally fail, resulting in a network outage. When a segment fails, an alarm is raised at the restoration node to which it is connected. For example, a segment that is a buried fiber optic cable may fail as a result of being inadvertently severed by someone digging near the buried cable. If one or more of the cables fail, massive disruption of services to a large number of network customers could result. Therefore, telecommunications carriers strive to quickly and economically route the network traffic around such failed components by establishing a "restoral" route. A restoral route is a path between the endpoints that does not include the failed component. The establishing of a restoral route generally involves: (1) detecting that a component on the current route has failed, (2) identifying the location of the component, (3) selecting a restoral route to bypass the failed component, and (4) implementing the selected restoral route. The reliability of telecommunication networks depends in large part on the ability to detect such failures and implement the restoral route with minimal impact on network customers. A plan that identifies which restoration nodes are to be switched to bypass one or more specific failed components is called a "restoration plan."
The implementation of a restoration plan is typically controlled from a central location. That central location is responsible for coordinating notification of segment failures, determining when a restoration should be initiated, and sending messages to the appropriate restoration nodes in order to effect the necessary connections. It would be desirable to have a mechanism for initiating a restoration without the need for a central location to determine when to initiate the restoration. Such determination is helpful when the implementation of a restoration plan is carried out in a distributed fashion. In a distributed restoration system, each restoration node detects segment failures and makes those connections to spare segments necessary to bypass that failure. Because these actions are carried out in separate restoration nodes, there are timing and synchronization problems in a distributed restoration system that are not present in a centralized restoration system.